Closed-cycle gas engine



A. J. SCHWEMIN 3,478,511

CLOSED- CYCLE GAS ENGINE Nov. 18, 1969 3 Sheets-Sheet 1 Filed July 15, 1967 irrazvlrff Nov. 18, 1969 A. J. SCHWEMIN 3,478,511

CLOSED-CYCLE GAS ENGINE Filed July 13, 1967 5 Sheets-Sheet 2 HP FIJI F tw M: F 4 Ira-claw;

Nov. 18, 1969 Filed July 15, 1967 FIG-.7

450v: Pure/v PPEJJUPFl .Eiww 7/570 FIG-6 A. J. SCHW EMIN CLOSED-CYCLE GAS ENGINE 3 Sheets-Sheet 5 FIG-5 lrram/iri United States Patent U.S. C]. 6024 1 Claim ABSTRACT OF THE DISCLOSURE The invention disclosed and claimed herein is an improved heat engine operating on a new closed cycle that in certain respects is similar to a Stirling cycle. The engine hereof includes a plurality of pistons with external heating and cooling of an operating fluid, means interconnecting successive pistons and individual pistons being operated by pressure differential thereacross resulting from a phase difference in pressures in the volumes above and below the pistons. A preferred physical embodiment of the invention, disclosed herein, incorporates a plurality of cylinders, preferably four or five, with a movable piston in each cylinder, and one end of each cylinder being connected through a heater, a regenerator and cooler to the opposite end of the adjacent cylinder. Heat is externally applied to or adjacent the first or hot end of each cylinder, and the entire engine is charged with an inert gas in a closed system whereby each piston then serves both as a power piston and displacer piston in the terminology of Stirling-cycle engines; each piston delivers power at two portions of each cycle. Control may be provided by varying the amount of gas in the closed system of the engine; and, in common with other types of heat engines, the present invention may be externally driven to move the pistons as a compressor for refrigeration.

BACKGROUND OF INVENTION Although the present invention operates on a novel heat cycle, it is sufficiently similar to the know Stirling cycle that extensive reference is made to such cycle in the following description. The Stirling cycle, or a modification thereof known as the Erickson cycle for hot-gas engines, has long been known in the art; reference is made to standard texts for a general description of the theory of operation thereof. In brief, a Stirling-cycle engine employs a closed gas system wherein the gas is heated to expand at a high temperature with useful work being extracted therefrom, or, alternatively, the engine may be driven to provide refrigeration. Although any desired source of heat may be employed for raising the temperature of gas in the engine, it has generally been considered practical to employ the combustion of a fossil fuel. In addition to standard engineering texts, reference is made to the publication, Phillips Technical Review, volume II, pages 245 to 276, for a general discussion of a Stirlingcycle engine and drive mechanism associated therewith.

Despite the fact that the Stirling cycle has long been known in the art, certain disadvantage thereof have seriously limited applicability on a wide scale. This type of engine operates by displacement of a gas from one end of a piston to the other; this has been accomplished by the utilization of a displacer piston operating in conjunc tion with a power piston for each cylinder. Despite certain undoubted advantages of this cycle, the requisite complexity and bulkines of mechanism for carrying out the cycle have limited its use. Additionally, difficulties have been encountered in translating the power output into useful motion: one solution to this latter difliculty is presented in the above-noted Phillips publication wherein there is described a novel rhombic drive mechanism. Previous attempts at the design of a Stirling-cycle engine employ- 3,478,51 1 Patented Nov. 18, 1969 ice ing only a single piston per cylinder have proven, at least in part, unsuccessful as evidenced, for example, by the above-noted publication.

The general field of hot-air engines, or hot-gas engines, has been extensively exploited, as is evidenced, for example, by the large number of existing patents in the field. A substantial number of U.S. patents has been issued during the present and last century for improvements in closed-cycle, hot-gas engines. Exemplary of these are relatively recent patents issued to Meijer, U.S. Patent No. 2,963,854, and Goebel et al., U.S. Patent No. 2,397,- 734, wherein the necessity of employing a pair of pistons per cylinder is recognized and set forth. U.S. Patent No. 2,326,901 to Thompson specifically relates to the Erickson cycle, which is substantially the same as the Stirling cycle, and also identifies the necessity of both transfer and work ing pistons, while the recent patent to Drumm, U.S. Patent No. 3,009,315, specifically identifies an improved heat engine operating on the Erickson heat cycle, or Stirling cycle, but yet employing both transfer and working pistons.

SUMMARY OF INVENTION There is provided by the present invention a hot-gas engine having a closed cycle with external heating and cooling and operating upon a particular cycle characterized by certain distinct features.

The engine has several cylinders, preferably four or five. The hot-gas volume at the top of each cylinder is connected to the cold-gas volume of its adjacent cylinder via a sequence of hot heat exchanger, a thermal regenerator, and a cold heat exchange, or cooler. Each piston of the engine then operates on two different pressures, i.e., the pressure above the piston and the pressure below the piston. The pressure operating on the top of the piston is controlled by the volume of hot gas over the piston and the volume of cold gas under the connected piston of lagging phase. The pressure operating on the bottom, or underside, of each piston is controlled by the cold volume under this piston and the hot volume over the connected piston of the leading phase. Inasmuch as the pressures in the two sets of above-identified volumes are out-of-phase, the pressures are unequal and generate a force on the piston. In the absence of heat being applied to the engine, no work is performed thereby; however, with the application of heat, it may be considered that a phase shift in the pressure curve results, so that a net, positive output is obtained. The present cycle provides for two power strokes per piston per revolution; it is particularly noted with respect to conventional Stirling-cycle engines that no separate displacer piston is employed herein. Furthermore, the engine hereof has essentially no unswept volume of gas to contribute to the inefliciency of the cycle.

In connection with the improved cycle of the present invention, there is also employed a simplified drive system utilizing a wobble-plate type of drive mechanism rotated by the piston rods. The cycle of the present invention produces a gradual increase and decrease in pressures, so that no great impacts are involved, as would result from explosions or rapid burning of fuels inside a chamber. This has the advantage of minimizing the mechanical strains, reducing weight and almost entirely eliminating noise. Engine efficiency is increased with increasing temperatures of operation; it is possible, in accordance herewith, to achieve very high engine efliciencies well in excess of conventional engines.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages of the present invention will become more apparent from the following description of the preferred embodiment thereof, when read in conjunction with the accompanying drawings in which:

FIGURE 1 is an end view of a five-cylinder, closedcycle gas engine constructed in accordance with the present invention and showing the tops of the cylinders;

FIGURE 2 is a reduced scale side-elevational view of the engine of FIGURE 1 with the engine being in horizontal position and the tops of the cylinders being at the right of the figure;

FIGURE 3 is a cross-sectional view taken along the folded lines 3-3 of FIGURE 1;

FIGURE 4 is a cross-sectional view taken along the folded lines 44 of FIGURE 1;

FIGURE 5 is a schematic view illustrating the cycle of operation of the piston within each of the cylinders of the engine of FIGURES l4; and

FIGURES 6 and 7 are graphic representations of engine characteristics with and without the application of heat.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, and particularly to FIG- URES 1 and 2, there is shown a closed-cycle gas engine 10. Various components of this engine are similar in structure and function to components employed in a Stirling-cycle engine and are thus, in part, referenced thereto. A full decription of the engine operation follows the description of the illustrated embodiment.

The engine 10 is constructed of five cylinders 12, I4, 16, 18 and 20 mounted in circular arrangement on a circular base plate 22. Each of the cylinders 1220 is mounted within a perpendicular bore 23 (see also FIG- URE 3) in the plate 22. The cylinders 12-20 are all of the same design; all are mounted on the plate 22 in the same manner. Therefore, only the cylinder 12 and the engine structure closely associated therewith will here be specifically described.

The cylinder 12 provides a sidewall 24, FIGURE 3, which defines the cylinder chamber 25. The top or outerend portion 26 of the sidewall 24 is surrounded by a cylindrical jacket 28. The wall portion 26 and jacket 28 together serve to define a gas-heating chamber 30 located therebetween. Mounted on the jacket 28 is a heating coil 32 which is of conventional type. The coil 32 surrounds the jacket 28 and is maintained in place by cylindrical retainer wall 34. Communication is thus provided as between the cylinder chamber 24 and the heating chamber 30. The cylinder 12 is supported at the sidewall 24 by means of a bracket 37 bolted to the top surface 38 of the plate 22.

Within the cylinder chamber 24 is positioned a piston 40, from the inner end 42 of which extends a piston rod 43. The piston 40 is constructed of a material of low-thermal conductivity such as, e.g., stainless steel. The piston 40 is of a length which is comparatively great with respect to the length of the chamber. Thus, the piston 40 preferably extends through almost fifty percent of the length of the chamber 25. The piston 40, adjacent the inner end 42 thereof, is provided with a circumferential recess 44. Positioned within the recess 44 is a sealing ring 46, constructed of suitable material, such as, e.g., a high-temperature O ring. The ring 46 bears against the inner surface 48 of the cylinder wall 24 so as to form, together With the latter, a gas-tight seal.

The cylinder 12 is closed at its lower, or inner, end by suitable sealing means 50 about the piston rod. The cylinder sidewall 24, at the inner-end portion 51 thereof, is formed with an external circumferentially-extending recess 52. A plurality of circumferentially-spaced-apart radial apertures 53 are provided in the wall 24 and aligned with the recess 52. The inner-end wall 50 is formed with a central aperture 54 through which passes the piston rod 43.

The heating chamber 30 is in communication, by means of a gas conduit 56, with the outer end 57 of a regenerator 58 mounted on the plate 22. The regenerator 58 may be of conventional design and provides a cylindrical chamber 60 within which is positioned a plurality of screens 61, being of a material such as copper which is suitable for the rapid exchange of heat with a gas in contact therewith. The screens 61 are maintained mutuallyspaced apart by a plurality of spacer rings 62 constructed of stainless steel. The regenerator will be understood to serve the purpose of removing heat from hot gas passing downward therethrough and returning this heat to gas passing upward therethrough.

At its inner end 63 the regenerator 58 is sealed to the plate 22 by a sealing ring 64 and communicates with the outer end 66 of a gas cooler 68 in the plate. The cooler 68 is formed of a plurality of screens 69, similar to 61, and is positioned within a suitable cylindrical depression 70 located at the top surface 38 of the plate 22. The screens 69 are cooled by the conduction of heat therefrom through the plate 22. Such heat is conducted away from the plate 22 by means of a, cooling coil 71. The coil 71 surrounds the plate 22 and contains :a circulating cooling liquid such as water.

A suitable gas, such as helium, is provided in the engine through a restricted passage 73 of FIGURE 4 at the lower end of 72 of the cooler. The passageway 73 in the plate 22 communicates with a chamber 74 that is defined by an indentation in the undersurface 75 of the plate and an attachment member 76 bolted to the plate. Gas is fed to the chamber 74 through an inlet pipe 77 and a passageway 78 within the plate 22. The gas is r ceived from a suitable high-pressure reservoir 79.

The gas within the reservoir 79 is maintained under a comparatively high pressure. Gas is supplied to the engine from the reservoir 79 through a pipe 80 having a control valve 81 therein and connected to the inlet pipe 77. Gas may be returned to the high-pressure reservoir 79 by a pump 82 from a low-pressure reservoir 83 connected to the pipe 77 by a control valve 84. Each of the coolers is connected to the chamber 74 by small restrictive apertures 73, so that each cylinder may be charged and the amount of gas in them varied. A main passage 85 extends from the bottom of collar 68 to its lower end of the next cylinder.

The cylinder 12 extends through the plate 22 to the under surface 75 of the latter. Formed in this undersurface 75 is a cylindrical depression 86 which is concentric with the -bore 23. Received within the depression 86 is the inner-end portion 51 of the cylinder wall 24. A retaining member 87, provided with a sealing ring 88, serves to seal the inner-end portion 51 of the wall 26 within the depression 86. The depression 86 and the retaining member 87 are of such dimensions that they define an annular opening 90 within the plate 22 surrounding the recess 52 and apertures 53. Opening into the annulus 90 is the lower end 91 of the passageway 85 which extends from the cooler 86 associated with the adjacent cylinder 20.

The retaining member 87 provides a piston-rod support box 92. The box 92 is formed with a central bore 94 through which the piston 43 passes. The box 92 supports two sets of roller bearings 96, 97 rotatably mounted therewithin. The bearings of sets 96, 97 project into the bore 94 and provide a bearing surface for the piston rod 43.

As shown in FIGURE 2, the piston rod 43 at its outer end 98 slideably engages the edge of a wobble plate 100 of conventional type. The wobble plate 100 is obliquely mounted on a rotatable drive shaft 102. The shaft 102, at its inner end 104 (see FIGURE 4) is rotatable within a suitable bearing member 106 mounted within the attachment member 76. Secured to the plate 22, at the undersurface 75 thereof, are the respective inner ends 108 of a plurality of cylindrical-mounting struts 110. Each of the struts 110, at is outer end 112, is secured to a support plate 114. The drive shaft 102 passes through the plate 114 and is carried in a bearing thereat so as to be rotatably mounted.

Considering the illustration of FIGURE 5, it will be seen that the five cylinders are illustrated with the piston of each in proper relative position. In this illustration, the separate cylinders are shown as being disposed in a single flat plane for clairity; thus, the first cylinder is repeated in dotted form to complete the circle. The end of each piston rod moves back and forth as though following a sine wave, illustrated at 116 of FIGURE 5; the last point thereon will be seen to correspond to the first, as should be the case with the last illustrated cylinder and piston being a reproduction of the first. It is also possible to consider the illustration of FIGURE 5 as showing successive positions of a single piston in one cylinder; engine operation is described in this connection below.

In the operation of the engine 10, each of the pistons 40 is double acting, serving as both a power piston and a gas displacer. The portion of each cylinder chamber 25 above the respective piston 40 provides a hot space. The portion of each cylinder chamber 25 below the respective piston 40 provides a cold space. Each of the pistons 40, in its operation, moves through a complete sine waveof motion, being represented by a cycle of five positions A, B, C, D and E (see FIGURE 5). The pistons 40 of each pair of adjacently-positioned cylinders 12-20 operate in tandem. Such operation will now be described with particular reference to cylinder 12.

Gas entering above the piston has been heated by picking up heat from the regenerator and is further heated by the heater, so as to expand above the cylinder at high temperature and, consequently, force the cylinder downward. This force is applied through the piston rod to the wobble plate for rotating same to consequently rotate the drive shaft. At the same time as work is being performed by the expansion of gas at high temperature above the piston, relatively cool gas below the piston is being forced out of the cylinder through the passage 85 and through the adjacent regenerator to the top of the next cylinder. When the piston reaches the bottom of its stroke, it has displaced substantially all of the cool gas from beneath the piston into the next adjacent cylinder; expansion of the gas in this adjacent cylinder at high temperature then forces the piston therein down. Proper phasing of the pistons results in the application of a substantially continuous force by the piston rods to rotate the Wobble plate. This rotation of the wobble plate also causes the individual pistons to be successively moved up, so as to transfer gas above the piston through the regenerator and cooler to the underside of the piston in the next adjacent cylinder. As the gas is transferred from an individual cylinder 12 by upward movement of the piston therein, it will be seen that the gas gives up heat in the regenerator and is further cooled in the cooler, so as to thus enter the lower end of the next adjacent cylinder in a relatively cool state. It will be seen that relatively cool gas beneath a piston is compressed as the piston moves down, and is thus forced back through the cooler and the regenerator where it picks up heat and is further heated in the heater to pass into the top of the adjacent cylinder for expansion at high temperature therein. Consequently, it will be seen that the piston of each cylinder operates both as a power piston and as a displacer piston.

In the position A, the piston 40 is moving up and continues such movement until it reaches an uppermost position within the chamber 25, as shown at B. As the piston 40 begins its downward stroke, gas flows into the chamber 25 above the piston. Such gas is received from the regenerator 58 through the conduit 56 and chamber 30 into the open cylinder end 36. Such gas has picked up heat in the regenerator 58 and it has been further heated during passage through chamber 30 by the heater 32. The hot gas, as it enters the open cylinder end 36, expands, and thus applies pressure to the piston 40. Such pressure serves to urge the piston 40 down and through the positions of its downstroke shown at C and D. At the same time, gas below the piston 40 is compressed and is forced from the chamber 25 through the apertures 53, through the chamber 90 and into the passageway 85. Such gas flows into the chamber 25 of the cylinder 20, after passage through the regenerator 58 associated with the latter.

After the piston 40 has reached its lowermost position, shown at B, it begins its upward stroke for return to the position A. During such upward stroke, the piston 40 forces gas from the chamber 25 above the piston. Such gas passes through the open cylinder end 36, the chamber 30 and the conduit 56 and into the regenerator 58. In the latter, the gas is cooled by giving up heat to the screens 61. The gas then passes from the inner end 63 of the regenerator 58 and into the cooler 68. The gas is there further cooled by contact with the screens 69. The gas then passes through the passageway and into the chamber associated with the cylinder 14. At the same time, gas enters the cylinder 12 beneath the piston from the associated chamber 90 through the apertures 53. Such gas has been received from the regenerator 58 and cooler 68 associated with the cylinder 20 through the intermediate passageway 85. When the piston 40 has returned to the position A, the cycle already described is then repeated.

The expansion of gas at high temperatures above the piston 40, at the same time that gas is compressed at low temperature beneath the piston 40, results in the production of useful work. The performance of the engine 10 is illustrated by the curves I, II, III and IV of the graph of FIGURE 7. Here, gas pressure is plotted as the ordinate. Each of curves IIV is drawn for the cycle of piston positions AE, illustrated in FIGURE 5.

The curve I represents the pressure in the hot space above the piston 40. The curve II represents minus the pressure in the cold space below the piston 40 (it is of course curve I inverted and delayed 360/5). The curve III represents the difference between the respective pressures of the curves I and II, therefore, the effective force obtained. The curve IV, which bounds the shaded area, represents the torque transmitted to the shaft 102. Such torque is equal to the effective force at any point along curve III, multiplied by the slope (i.e., the cosine of the angle) of the curve III at such point. Without the application of heat the same curves look like those in FIGURE 6 wherein no useful work results.

With regard to practical operation of an engine in accordance with the present invention, it is noted that a wide variety of different heat sources may be employed. The illustrated embodiment of the present invention employs heater coils; however, this is only illustrative of a heat source rather than indicative of a preferred manner of applying heat. It is to be appreciated that substantial quantities of heat are to be available; furthermore, that a maximum transfer of heat to the gas entering the top of of each cylinder is highly advantageous. It is, thus, possible to employ some type of open burner utilizing the heat of combustion of fossil fuel, for example, and to transfer heat through any of various types of heat exchanges to gas entering the top of the cylinders. One particularly advantageous heat source is a small nuclear reactor of the type relatively recently developed for the production of substantial amounts of heat without the requirement of frequent recharging. The present invention is particularly adapted for utilization with this type of heat source, and provides a highly efficient manner of obtaining useful work therefrom. It is additionally noted that insofar as practical applications of the present invention are concerned, it is preferable to charge the cylinders with some gas other than air. In operation, it is intended that the closed and sealed engine shall be initially evacuated to remove as much air as possible from the cylinders; then, the engine shall be charged with a gas such as helium or possibly hydrogen. Although the engine operates upon a closed-gas cycle, it is advantageous to provide a system such as illustrated in FIGURE 4 to vary the amount of gas within the engine. This, then, provides a simple, rapid and effective means of controlling the output of the engine. In general, it is not feasible to vary engine operation by changing the temperature gradient; consequently, the present invention provides for varying the amount of gas employed therein. As the amount of gas is increased, the power output of the engine rises. This is herein accomplished by admitting more gas under high pressure to the engine. Power is decreased by reducing pressure of gas within the engine by returning some of the gas to the reservoir 79. As illustrated in this FIGURE 4, the valves 81 and 84 may be operated, possibly from a single con-- trol, to connect the high-pressure reservoir to the small chamber 74 that is, in turn, connected through restricted passages 73 to each of the cylinder coolers. Such a connection will cause the amount of gas in the engine to change rather rapidly, i.e., within a few seconds. It is to be particularly noted that the passageway 73 from the coolers to the chamber 74 has a very small cross section; thus, during normal engine operation almost no flow of gas occurs therethrough between coolers of separate cylinders. In order to reduce the power output of the engine, it is only necessary to open the valve 84 While energizing the pump 73, so as to withdraw gas from the engine and return it at high pressure to the reservoir 79 for storage.

The engine 10 provides a number of structural and operational advantages, as compared to closed-cycle engines of the prior art. Thus, the engine 10 is unusually compact in its organization. Such compactness results from the manner of mounting of the cylinders 1220 and of the other elements of the engine structure on the plate 22. In addition, the engine 10 provides an operable single, double-acting piston which exhibits no leakage problem. As a further advantage provided by the engine 10, an unusually high ratio of horsepower-to-engine-weight is obtained. A number of the design features of the engine 10 aids in preventing heat loss. Thus, the material of construction of each piston 40, and the unusually great length thereof, serves to minimize loss of heat through the piston 40. The sealing rings 64 and 88 serve to minimize heat loss from the cooler 68 and chamber 90, respectively. The drive system of the engine 10, including the piston-rod stabilizing bearings 96, 97 and the wobble plate 106, provides a comparatively simple yet extremely effective means for utilizing the engine power. If desired, the engine 10 may be modified in structure by a change in the number of cylinders therein. As a further modification, a ridge (not shown) may be built into the jacket 28 associated with any of the cylinders 12-20, so as to increase the volume of the respective chamber 30. Faster movement of gas through the chamber 30, and better heating of the gas therein, would result. If desired, the engine 10 may be modified in structure so as to be suitable for use as a refrigeration system.

Although the invention has been described with reference to particular embodiments thereof, it will be understood that various changes and modifications may be made therein without departing from the spirit of the invention or the scope of the appended claim.

That which is claimed is:

1. In a hot-gas engine including means defining a plurality of cylinders adapted to contain a gas and each containing a reciprocally-mounted piston, heat exchange means at a first hot end of each cylinder for the application of heat to gas therein, means connecting the first hot end of each cylinder with a second cold end of an adjacent cylinder to form a closed loop and such means each including a regenerator connected to a first hot cylinder end and cooler connecting the regenerator to a second cold cylinder end, and means mechanically interconnecting said pistons and causing same to reciprocate in relative phase-shifted relation; the improvement comprising:

(a) a high pressure gas reservoir;

(b) means defining a chamber having restricted passages communicating therefrom to each cylinder separately at the second cold ends thereof;

(c) a conduit having a valve therein connecting said gas reservoir to said chamber; and

(d) a gas return line including a valve connecting said chamber to a pump through said reservoir.

References Cited UNITED STATES PATENTS 2,272,925 2/ 1942 Smith 24 XR 2,611,235 9/1952 Van Weenen 60-24 2,616,242 11/1952 Horowitz et al. 6024 2,664,699 1/1954 Kohler 60-24 3,183,662 5/1965 Korsgren 60-24 FOREIGN PATENTS 131,359 4/1951 Sweden.

OTHER REFERENCES Phillips Technical Review, 1947, vol. IX, No. 5, pp. -160.

MARTIN P. SCHWADRON, Primary Examiner R. R. BUNEVICH, Assistant Examiner US. Cl. X.R. 

